In an electric rotating machine such as an electric motor, a rotor may be provided with salient poles projecting along the radial direction that is perpendicular to the rotational axis, which are arranged along the circumferential direction at predetermined intervals. A reluctance motor is one example of a conventionally known electric rotating machine having such a rotor including salient poles. With the salient poles being arranged along the circumferential direction, portions having low and high reluctance, i.e., magnetic resistance, are provided alternately along the rotor circumferential direction. By creating a rotating magnetic field around such a rotor by means of a stator, the salient poles are attracted to the rotating magnetic field, such that torque for rotating the rotor can be generated.
In a reluctance motor, the rotor is not provided with a permanent magnet. A reluctance motor is a motor that generates torque from differences in reluctance as described above. This motor is low-cost because the cost of a permanent magnet, which is not required, can be eliminated. Because a permanent magnet is not required, it is also unnecessary to provide a structure for fixing a permanent magnet on the rotor, thereby enabling further simplifying of the structure. It is obviously also unnecessary to consider the possibility of the permanent magnet being detached from the rotor due to centrifugal force caused by rotation, and the motor is suitable for use at high rotational velocity. Because of these advantages, reluctance motors are regarded as prospective power sources for use in automobiles, for example.
However, in an electric rotating machine in which salient poles are arranged on the rotor, a disadvantage is caused in that, when the rotor is rotated, the salient poles agitate air around the rotor. Particularly during high-velocity rotation, as compared to in an electric rotating machine in which the rotor has a substantially cylindrical shape, rotational resistance due to air agitation is undesirably increased.
For the purpose of reducing this rotational resistance, a technique of covering the portions between adjacent salient poles at a rotor end face is conventionally known. For example, according to the electric motor described in Japanese Patent Laid-Open Publication No. Hei 11-69674, a disc-shaped plate member is provided at an end portion along the axis direction of a rotational shaft of the rotor core, so as to prevent air from moving in and out between the grooves between the salient poles of the rotor and the outside space beyond the rotor end face in the rotational axis direction, thereby reducing rotational resistance due to air agitation caused during rotor rotation.
In electric rotating machines as described above, in order to lubricate the bearing supporting the rotational shaft of the rotor and to cool the rotor and the stator, lubricating oil may be supplied to these parts from outside. Such electric rotating machines generally operate in a state in which the lubricating oil is present at the bottom portion within the housing.
When an electric rotating machine employing this type of lubricating system is configured with a rotor having the above-noted salient poles, the lubricating oil may flow into the groove-shaped gaps (hereinafter referred to as “slots”) between the adjacent salient poles, such that the salient poles would hit on the lubricating oil, causing rotational resistance of the rotor. This rotational resistance of the rotor due to agitation of lubricating oil (hereinafter referred to as “oil agitation resistance”) is extremely large compared to when agitation occurs with respect to air alone. Particularly when the rotor is rotated at a high velocity, the oil agitation resistance becomes serious, resulting in a large decrease in the torque output from the electric rotating machine. When the electric rotating machine is mounted on a vehicle as a power source, the oil agitation resistance would be a factor causing degradation in fuel consumption. Accordingly, in electric rotating machines, a technique for reducing oil agitation resistance during high-velocity rotation is particularly desired.
The present invention provides an electric rotating machine in which flow of a lubricant oil into the slots between adjacent salient poles is restrained so as to enable reduction of oil agitation resistance during high-velocity rotation.